GOLDEN POND, Kentucky (AP) – Like a slow-motion, underwater cattle drive, wildlife officials in a half-dozen aluminium boats used pulses of electricity and sound on a recent grey morning to herd schools of Asian carp toward 1,000-foot-long nets.
The ongoing roundup on wind-rippled Kentucky Lake opens a new front in a 15-year battle to halt the advance of the invasive carp, which threaten to upend aquatic ecosystems, starve out native fish and wipe out endangered mussel and snail populations along the Mississippi River and dozens of tributaries.
State and federal agencies together have spent roughly USD607 million to stop them since 2004, according to data compiled by The Associated Press. Projects in the works are expected to push the price tag to about USD1.5 billion over the next decade.
That’s more than five times the amount predicted in 2007 when a national carp management plan was crafted, and no end is in sight. Programmes aim to reduce established populations and prevent further spreading, but wildlife officials concede they may never be able to eradicate the prolific fish.
Much of the focus has been on limiting their northerly migration and keeping them out of the Great Lakes, where experts said they could devastate a USD7 billion fishing industry. That effort features an underwater electric barrier near Chicago, water sampling for carp DNA, subsidies for commercial fishers and experiments with a mass roundup-type harvest.
It has been largely successful, although the lakes remain vulnerable and grass carp — one of the Asian varieties — have been spotted in Lakes Erie, Ontario and Michigan.
Less money and attention have been paid to the carp’s virtually unchecked spread east and west into the Missouri and Ohio rivers, among others.
Asian carp were imported to the United States (US) in the 1960s and 1970s as an eco-friendly alternative to poisons for ridding southern fish farms and sewage lagoons of algae, weeds and parasites. They escaped through flooding, deliberate stocking and other means.
“It was a dumb idea,” said President of the advocacy group Alliance for the Great Lakes Joel Brammeier. “Even back then, biologists understood the risks of bringing live, non-native animals into the country. It should never have happened.”
Greg Conover, a US Fish and Wildlife Service biologist who oversaw development of the national Asian carp strategy, realised how abundant they were becoming in the Mississippi River as he studied native paddlefish in the 1990s.
“At first there were no carp, then we were catching a few carp here and there, then eventually we were filling the nets with carp and no paddlefish,” he said.
The catchall term “Asian carp” refers to four different invasive species — bighead, black, grass and silver carp. Sport anglers are feeling their impacts. Scientists reported that carp in the upper Mississippi are out-competing prized native fish such as yellow perch and bluegill. And silver carp hurtle from the water like missiles when startled by boat motors. Collisions have broken noses, jaws and ribs.
“That has hurt the tourism industry,” said Kentucky’s Aquatic Nuisance Species Programme Director Ron Brooks.
There are no precise estimates of Asian carp populations in US waters, but there are believed to be millions. At times, they’ve totalled up to 90 per cent of all fish populations on some backwaters of the Mississippi River. On two large reservoirs in Kentucky last year, commercial fishermen brought in six million pounds of Asian carp.
Asian carp are established in much of the central US. They grow quickly and reproduce abundantly; females lay up to five million eggs at a time. Silver carp mature in three to four years and can grow to about 60 pounds. Bighead, the largest, can reach 110 pounds.
Grass carp — the only Asian carp species that can still be legally imported for weed control — have been found as far west as Utah, and in Florida and New York.
Early attempts to rein in Asian carp were slow going. “For years we couldn’t even catch them,” said Fisheries Chief of the Tennessee Wildlife Resources Agency Frank Fiss. “We had to adapt our gear to get the right gill nets, the right electroshocks. There was a steep learning curve.”
Some fish farmers didn’t want the carp banned. States were slow to act. One control method, commercial fishing, hit a snag when processors realised that while the carp are a prized food in China, buyers there like them fresh, not frozen.
But control efforts are increasing and becoming more successful. In the upper Illinois and Des Plaines rivers last year, a combination of the roundup method and commercial fishing helped pull in 1.5 million pounds of carp, said Aquatic Nuisance Species Manager with the Illinois Department of Natural Resources Kevin Irons. Irons said they have seen a 96.7 per cent drop in the Asian carp population on that stretch of river since 2012.
Still, the Illinois remains infested. To prevent carp from migrating northward into Lake Michigan, the US Army Corps of Engineers is proposing the priciest initiative yet: fortifying a lock and dam on the outskirts of Chicago with an electric barrier, underwater speakers blasting irritating noises, and air bubble curtains. The project, awaiting congressional approval, could cost more than USD800 million.